Non-volatile memory cells are widely used because they can store data even when the power supply is cut off Generally, non-volatile memory cells can be sub-classified into two types, floating-gate structure and SONOS structure. The floating-gate structure utilizes source side injection (SSI) or tunneling effect leading hot electrons stored in the floating gate.
However, the application of the floating-gate structure is increasingly difficult day after day, because of the hot electrons punching through along the select gate channel as the source-drain channel length shrinks. In comparison with the floating-gate structure, the SONOS structure which also leads hot electrons stored in a silicon nitride layer, can be manufactured in a smaller critical size by simpler processes, by which functions of multi-level storage are provided to overcome the drain-induced turn-on effect. Therefore, there is a prevailing tendency today to replace the floating-gate structure with the SONOS structure.
However, for the purpose of improving the performance of the non-volatile memory cells, there are still a number of challenges presented to the industry in terms of improving the programming and erasing (P/E) speed, decreasing the operation voltage and improving the reliability of the SONOS structure.
Therefore, there is a need of providing an improved memory device and the fabricating method thereof to obviate the drawbacks encountered from the prior art.